Method of constructing liquid-tight side wall containers

ABSTRACT

A LIQUID-TIGHT SIDE WALL AND METHOD OF CONSTRUCTION ARE DESCRIBED IN WHICH AN INNER PLASTIC LINER IS ADHERED TO THE INTERIOR OF AN AIR-PERMEABLE CONTAINER SIDE WALL BY THE USE OF VACUUM FORMING AND A HEAT-ACTIVATABLE ADHESIVE.

Feb. 9, 1971 I w. KOUDSTAAL 3,562,055

METHOD OF CONSTRUCTING LIQUID-TIGHT SIDE WALL CONTAINERS Filed Sept. 11. 1967 \5 I I i l a I E m \7- I l 2A a M N INVENTOR WILLEM Rows-MAL United States Patent 3,562,055 METHOD OF CONSTRUCTING LIQUID-TIGHT SIDE WALL CONTAINERS Willem Koudstaal, Spijkenisse, Netherlands, assignor to Inland Steel Company, Chicago, 11]., a corporation of Delaware Filed Sept. 11, 1967, Ser. No. 666,830 Claims priority, application Great Britain, Sept. 13, 1966, 40,790/ 66 Int. Cl. B29c 17/06 U.S. Cl. 156-287 9 Claims ABSTRACT OF THE DISCLOSURE A liquid-tight side wall and method of construction are described in which an inner plastic liner is adhered to the interior of an air-permeable container side wall by the use of vacuum forming and a heat-activatable adhesive.

DESCRIPTION OF THE INVENTION The present invention relates to the art of making shipping containers, and in particular to shipping containers for transporting liquids.

Shipping containers of the general type concerned here, commonly comprise a cylindrical body having a reinforced inwardly extending circumferential bead and a chime at each end, with the ends being provided with suitable closures. Side walls for such containers may be formed of any suitable material, but in recent years increasing use has been made of fibrous material such as paperboard, cardboard, or the like. However, these materials are not generally liquid-tight and therefore attempts have been made to provide liquid-tight properties for side walls constructed of these materials. These techniques have included the use of a liquid-tight internal lining of flexible sheet material such as polyethylene.

The invention is not limited to use with container side walls formed of such material, but will also find use with steel or other imprevious side wall materials with certain modifications as described herein.

With plastic lining materials, difiiculties are often encountered in achieving a smooth fit and tight adherence to the container side wall, particularly in the vicinity of the chime. It is highly desirable to be able to form all convolutions in the side wall prior to the installation of the internal lining so as to avoid damage to the lining as a result of the forming process. Difiiculties have also been encountered heretofore in achieving a uniform degree of adherence throughout the inner surface area of the side wall where the internal plastic liner is to be attached. The liner has a tendency to remain stretched between the inwardly extending beads, or between one bead and the opposite chime end of the container rather that lying smoothly against the inner wall surface.

It is therefore a general aim of the present invention to overcome the foregoing difficulties and to provide an improved shipping container side wall and method of manufacture characterized in that the side wall is provided with a liquid-tight internal plastic liner which is drawn smoothly into contact with the internal surface of the container side wall, and then adhered thereto in a simple and reliable manner. It is further contemplated that the invention will provide a simple, efficient and inexpensive improved method for forming such a container side wall.

In another of its important aspects, it is an object of the invention to provide an improved method and apparatus for forming an internally lined container side wall of the character described characterized by exceptional versatility in that such methods and apparatus may find equal applicability in lining a wide variety of different types of side walls whether the latter are made of porous material such as fibre or of impervious material such as steel.

Other objects and advantages of the invention will become apparent as the following description proceeds, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a side elevational view taken in section in which an exemplary apparatus is depicted for forming lined shipping containers embodying the features of the invention, with a container and its lining being shown in an initial stage of the forming process; and

FIG. 2 is a side elevational view taken in section similar to FIG. 1 illustrating the insertion of a heating device as the formation of the container proceeds in an advanced stage of the forming operation.

While the invention is susceptible of various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawing and will be described herein in detail. It should be understood, however, that the invention is not intended to be so limited by the particular forms disclosed, but is intended to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as expressed in the appended claims.

Turning first to FIG. 1, there is shown in half-section an exemplary apparatus suitable for carrying out the method of the present invention, with a performed container side wall 10 contained therein in readiness for the forming operation by which an inner liner is to be adhered. The container side wall 10 is generally formed of fibrous, air-permeable material such as paperboard, cardboard or the like. Formation of such a side wall may be done in any known manner, such as by winding a plurality of layers of paper one on top of the other, either by convolute winding or by helical winding. A side wall 10 made in this manner is generally formed with a circurnferential external groove 11 which is complementary to an internal rib 12. Such a structure is formed adjacent both extremities of the side wall 10 and forms a part of the chime at each end.

The internal ribs 12 at each end of the container side wall may serve as a support for a closure such as a bottom or lid (not shown) which, together with the completed side wall 10, constitutes the finished container. For this purpose a rigid reinforcing ring 13 of metal is used to reinforce the side wall extremities. The closure may then be secured by crimping or by any other suitable means.

In carrying out the invention, the inner surfaces of the side wall 10 are prepared for the application of a liquidtight internal liner by applying an adhesive substance. This is preferably a heat activatable substance which acquires adhesive properties when heat is applied. Good results have been obtained by employing a dispersion or emulsion of ethylene and vinyl acetate copolymer, or alternatively a mixture of wax and tackifying resins in a thinner consisting of xylene, water, caustic soda and an emulgator kept at a temperature of about 50 C. or higher. Other adhesive substances having similar properties will also give satisfactory results.

The adhesive substance to be used is preferably sprayed onto the inner surface of the side wall 10, whereupon the side wall is heated to a temperature of about 70 or C. in a manner to be hereinafter described. The liquid contents of the dispersion or emulsion will evaporate, leaving the non-volatile components of the adhesive on the inner surface of the side wall 10 in the form of a thin deposit 14.

Pursuant to the invention, a sheet of liquid-tight plastic 15 is then drawn into intimate contact with the inner surface of the side wall 10 by a vacuum forming process.

This is accomplished by employing a length of extruded seamless plastic tubing 15 of a thermoplastic material such as polyethylene. The cross-section of the tubular liner 15 is preferably slightly smaller than the crosssection of the side wall, and in the illustrative embodiment, the liner 15 is approximately the same diameter as the inner diameter of the internal ribs 12 of the side wall 10. The tubular liner 15 is positioned within the side wall and the extremities of the liner are caused to engage the extremities of the side wall. In the illustrative example, the liner 15 is folded at each end over the ends of the side wall 10.

It should be noted that the inner liner 15 may be made of various materials and with differing construction. Any suitable sheet material may be used, such as polyethylene, polyvinyl chloride, or other similar liquid-tight material. It is formed preferably as a seamless extruded tube, or in the alternative fabricated into tube form from sheet material with a heat-sealed or taped seam where the ends of the sheet abut or overlap.

The side wall 10 with its inner layer of deposited adhesive 14 andthe liner 15 attached at each extremity is then placed in a rigid air-tight chamber 16 for the purpose of drawing the liner 15 tightly into contact with the adhesive layer 14 to form a liquid-tight internal coating. For this purpose the chamber 16 is provided with a bottom member 17 and a sealing gasket 18 made of rubber or other resilient material. The chamber 16 is closed by a removable annular lid 19 having a similar sealing gasket 20 whereby the extremities of the side wall 10 are clamped securely together between the gaskets 18, 20. The chamber 16 is then connected to a source of vacuum or suction (not shown) by a connection 21.

After the prepared container side wall 10 with its liner 15 has been clamped securely in the chamber 16, a heating element indicated generally at 22 is lowered into the interior of the side wall 10. The heating element 22 includes a plurality of tubular heating coil elements 23 supported by a tubular central column 24. The heating coils 23 may then be connected to a source of electrical energy (not shown). Preferably, the external surface of the central column 24 is highly polished, and a foot plate 25 and a head plate 26 are provided having surfaces which are also highly polished. The effect of these polished surfaces is to increase the efliciency of the heating element 22 in performing its function.

As the next step in carrying out the invention, the heating element 22 is energized and the amount of heat is controlled so that the adhesive layer 14 on the inner surface of the side wall 10 is activated. In the illustrative embodiment described, the melting or softening point of the plastic polyethylene liner material is about 100 C. or higher so that the adhesive layer 10 can be heated to this point without danger of unnecessarily softening the liner 15. When thus treated, the plastic liner 15 becomes plastically deformable in preparation for the next step of the forming method.

A vacuum is then applied to the chamber 16 through the connection 21. The space between the side wall 10' and the liner 15 is thereby evacuated as air is withdrawn through the air-permeable fibrous side wall material and out the connection 21. The liner 15 is thus drawn towards the inner surface of the sidewall 10 and becomes vacuum-formed into intimate engagement with substantially the entire adhesive-covered inner surface. Finally, the suction and heating are cut off and the heating element 22 is removed. The lid 19 may then be removed and the finished side wall 10 with its lining 15 securely adhered to its internal surfaces may be removed to a subsequent manufacturing station.

It will be apparent to one skilled in the art that the steps previously described may be efiected in a sequence other than that just described without departing from the invention. For instance, the side wall 10 with its 4 internal coating of adhesive 14 may be heated to activate the adhesive prior to being fitted with the internal liner 15 and prior to being placed within the vacuum chamber 16. The means used to activate the heat-activatable adhesive layer 1 4 on the inner surfaces of the side wall 10 may be the same heating apparatus 22 employed for the purpose of softening the plastic liner 15 prior to vacuum forming it against the side wall 10. As yet another alternative, the heating of the side 'wall 11 to activate the adhesive layer 14 may be delayed until after the chamber 16 has been evacuated, with the heating being applied while the plastic liner 15 is held tightly against the inner surface of the side wall 10 by the pres sure differential of the vacuum. Still another alternative is to cause heating and evacuation of the chamber 16 substantially simultaneously.

It should also be understood that the annular space between the side wall 10 and the liner 15 need not be evacuated by withdrawing air only through the permeable fibrous side wall material. The air within this space may alternatively be drawn through the many small annular passages which exist between the reinforcing rings 13 and the associated extremities of the side wall 10 as shown in FIG. 2, since it is seldom that the connection between these parts can be made completely air-tight. If required, one or more vent holes 27 may also be drilled in the reinforcing rings 14 to further facilitate the withdrawal of air, especially in the event that the side wall is made of steel or other impermeable material.

In this connection, it should be noted that the pressure within the vacuum chamber 16 need not be decreased to approach zero, as it will sufiice if the pressure differential between the chamber and the space between the side wall 10 and liner 15 is such that the liner is drawn into intimate contact with the adhesive layer 14.

As previously described, it is also preferable to form all grooves or beads such as the grooves 11 and internal ribs 12 prior to fitting the internal liner 15. In this way the lining will not suffer damage in forming or crimping operations used to form such elements.

The container side wall which is formed by the method of the present invention has the advantage that the lining of the side wall 10 is non-porous and liquid-tight. By comparison with the method of employing prelined kraft paper for forming such side walls, the invention has the advantage that the necessity of taping or otherwise sealing the side seam of the container is thus eliminated. By using a continuous extruded internal plastic liner 15 in connection with the invention, the need to deal with such seams is also eliminated. The result is thus a container side wall having an adhering seamless and continuous lining which is free of any wrinkles or other imperfections.

A complete container is then formed from the completed side wall 10 by securing suitable top and bottom closures (not shown). For this purpose, the internal ribs 12 may be used as supports against which the closures may be secured in known fashion.

What is claimed is:

1. The method of constructing a liquid-tight shipping container side wall comprising the steps of placing a liquid-tight tubular liner of impervious sheet material within a container side wall, said side wall having had applied thereto an inner coating of heat-activatable adhesive, engaging the extremities of the liner with the extremities of the side wall, activating the adhesive by the application of heat, and creating a pressure differential in the space between the side wall and the tubular liner, the pressure differential being sufficient to cause said liner to deform and to adhesively engage substantially the entire inner surface of the side wall.

2. The method according to claim 1 in which the airpermeable side Wall is of fibrous material.

3. The method according to claim 1 in which an inturned annular bead is formed at one inner wall end of said side wall prior to positioning said liquid-tight liner within said side wall.

4. The method according to claim 1 in which said tubular liner is of heat-softenable material, and said liner is heated prior to being deformed.

5. The method according to claim 4 in which the heat activation of said adhesive is accomplished substantially simultaneously with the heating of said tubular liner.

6. The method according to claim 1 in which said side wall is of impervious material having a plurality of perforated vents.

7. The method according to claim 6 in which an inturned annular bead is formed at one inner Wall end of said side wall prior to positioning said liquid-tight liner within said side wall.

8. The method according to claim 6 in which said tubular liner is of heat-softenable material, and said liner is heated prior to being deformed.

9. The method according to claim 8 in which the heat activation of said adhesive is accomplished substantially simultaneously with the heating of said tubular liner.

References Cited UNITED STATES PATENTS BENJAMIN R. PADGETT, Primary Examiner G. G. SOLYST, Assistant Examiner US. Cl. X.R. 2201.5 

